Son has to cry, seeing subject of The Water Babies (5)
I believe the answer is:
sweep
'seeing subject of the water babies' is the definition.
'sweep' can be an answer for 'seeing' (thesaurus). I am not certain of the 'subject of the water babies' bit.
'son has to cry' is the wordplay.
I cannot quite understand how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found within the answer.
'cry' could be 'weep' (synonyms) and 'weep' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sweep that I've seen before include "if clean, could result in a whitewash" , "do cleaning" , "range" , "Gamble - with brush!" , "Victorian child labourer" .)